3-Manifolds  

In General
* Topological classification: A full one has not been found yet, but various different decompositions are possible, the prime-decomposition, the torus decomposition and the Heegard decomposition.
* Prime decomposition: Any three-manifold can be decomposed in an essentially unique way as

3M = R3 # M1 # M2 # M3 # ... ,

where # stands for a connected sum, the initial R3 factor is present for the (topologically) asymptotically flat case, and each Mi is a "prime" manifold; Notice that, for non-orientable Mi's, the connected sum # does not specify in which of the two inequivalent ways the operation is performed (for the orientable ones, there is only one orientation-preserving possibility); The irreducible pieces Mi have not been classified (from Rafael, 03.1985).
* Cobordism: All closed 3-manifolds are in the same cobordism class.
* Differentiable structure: All closed 3-manifolds have a unique differentiable structure.
* Spin structure: All 3-manifolds admit a spin structure.
* Decidability: The set of compact 3-manifolds is algorithmically decidable, i.e., it has an algorithmic description.

Examples > s.a. laplace operator
* Lens spaces: 3D constant positive curvature manifolds, obtained as quotients of the three-sphere; Denoted by Lp,q:= S3/ , where S3= {(z1, z2) C2 | (z1, z2) = 1}, (z1, z2) ( z1, q z2), := exp{2i/p}, and p and q are relatively prime integers; S3 is a p:1 cover; Example: L2,1 = SO(3).
@ Lens spaces: Bellon CQG(06) [harmonics from holonomies, and cosmology].
@ Non-orientable: Amendola & Martelli T&A(03), T&A(05) [small complexity]; Casali T&A(04) [complexity].
@ Compact hyperbolic: Culler et al Top(98) [smallest]; Kramer ap/04 [group actions and symmetries].
@ Other: in Freed & Gompf PRL(91) [Brieskorn sphere]; Scannell CQG(01) [spacelike slices of flat spacetimes]; Bray & Neves AM(04) [prime, Yamabe invariant > RP3]; Boileau & Weidmann Top(05) [with 2-generated fundamental group].

Invariants > s.a. knot invariants; Turaev-Viro Theory.
* Complexity: The numbers of manifolds of complexity 0, 1, 2, 3, 4, 5, 6, respectively, is 3, 2, 4, 7, 14, 31, 74; The first hyperbolic 3-manifold occurs at complexity 9.
* Volume: For hyperbolic ones, with curvature normalized to –1; Problem: For each V, there are finitely many 3-manifolds with volume < V; Which is the smallest?
* Other: Reshetikhin-Turaev invariant; > s.a. topological field theories, including chern-simons, spin networks.
@ General references: Stewart Nat(89)mar [volume]; Reshetikhin & Turaev IM(91) [from links and quantum groups]; Kauffman & Lins 94; Bott & Cattaneo JDG(98)dg/97, JDG(99)m.GT/98 [integral]; Liu Top(99); Korepanov JNMP(01)m.GT/00 [PL]; Korepanov & Martyushev JNMP(02); Turaev 02 [torsion]; McDuff BAMS(06) [and Floer theory, Ozsváth-Szabó]; King T&A(07) [ideal Turaev-Viro invariant].
@ And topological quantum field theory: Bakalarska & Broda ht/99-in, FdP(00)ht/99; Ramadevi & Naik CMP(00) [Lickorish invariant and Chern-Simons theory]; Kaul & Ramadevi CMP(01)ht/00 [from Chern-Simons theory]; Garnerone et al qp/07 [in SU(2) Chern-Simons-Witten topological quantum field theory].
@ Finite-type: Garoufalidis et al G&T(01)m.GT/00 [and trivalent graphs].
@ Relationships: Guadagnini & Pilo CMP(98); Mariño & Moore NPB(99) [and 4D Donaldson-Witten invariants].
@ With boundary: Murakami & Ohtsuki CMP(97) [from universal quantum invariant].
@ Classification: Milnor AJM(62); Hendricks BAMS(77); Thompson BAMS(98) [algorithmic]; Morgan BAMS(05).
@ Related topics: Baseilhac & Benedetti m.GT/01; Harvey G&T(02) [cut number not bounded below by 1(X)/3], Top(05) [from fundamental group]; Ozsváth & Szabó AM(04) [and holomorphic disks]; Cavicchioli & Spaggiari DM(08) [genus-2, representation by family of integers].

Other Structure and Concepts > s.a. diffeomorphisms [including Smale conjecture]; embeddings; 3D geometry; knots.
@ General references: Gluck & Pan Top(98) [embedded 2-surfaces]; Neumann & Swarup G&T(97) [decompositions]; Camacho & Camacho T&A(07) [codimension-1 foliations]; Fernández & Mira DG&A(07) [constant mean curvature surfaces in homogeneous 3-manifolds].
@ Hyperbolic: Fenley Top(98) [foliations]; Gabai et al AM(03) [homotopy hyperbolic].

References > s.a. conjectures [Smith]; topological field theory.
@ Simple, or for physicists: Thurston & Weeks SA(84)jul; Giulini IJTP(94)gq/93; Thurston CQG(98).
@ Topology: Neuwirth 75; Hempel 76; Thurston 78; Jaco 80; Brown & Thickstun ed-82; Bing 83; Fenn ed-85; Thurston 97.
@ And computers: Lins 95 [gems].
@ Homeomorphisms: Cesar de Sa & Rourke BAMS(79).
@ Surgery / Links: in Rolfsen 76, ch9; Kirby IM(78).
@ Framings: Atiyah Top(90).
@ Related topics: Schoen & Yau PNAS(78), AM(79), PRL(79) & refs; Hendriks & Laudenbach Top(84); Friedman & Witt Top(86); Freedman & Feng 89; Gabai & Oertel AM(89); Crane CMP(91).


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